Relating to automatic injection devices

ABSTRACT

An injection device comprises a syringe extendible against a spring bias from a retracted position in a housing to a projecting injecting position. A spring biased plunger has collapsible elbows which, when the plunger is released, initially engage the end of the syringe to drive it to the projecting position, whereupon arresting of the syringe movement causes the elbows to collapse inside the syringe to allow the plunger to engage and drive the bung.

RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 14/109,363 filed on Dec. 17, 2013, which is a continuation ofU.S. patent application Ser. No. 13/443,384 filed on Apr. 10, 2012,which is a continuation of U.S. patent application Ser. No. 13/072,289filed on Mar. 25, 2011, which is a continuation of U.S. patentapplication Ser. No. 11/630,507 filed Jan. 7, 2008, which is a 35 U.S.C.§371 Application of PCT Patent Application Number PCT/GB2005/002487,filed Jun. 23, 2005, which claims priority to United Kingdom PatentApplication No.: 0414054.7 filed on Jun. 23, 2004. The entire contentsof each of the above applications are herein incorporated by referencein their entirety.

BACKGROUND

There are various forms of automatic injection device which whenoperated cause the needle of a syringe to be moved forwardly so that itprojects from a protective housing prior to actuation of the syringe toexpress a dose of liquid through the needle. It is important to try toensure that the syringe is moved bodily forward to expose the needlebefore the liquid charge is pressurised so that dribbling from theneedle does not occur before the actual injection takes place. It is anobject of this invention to provide a mechanism which operates in thisdesired manner.

SUMMARY

According to the invention there is provided an injection device forcausing a dose of liquid to be ejected from the needle at one end of asyringe located within a housing of the device, the syringe beingmovable by a plunger, upon release of an actuating bias member at oneend of the housing, to move the syringe, from a first position whereinthe needle is shrouded by the housing, to a second position wherein theneedle projects from the other end of the housing, the plunger being inthe form of a rod with a longitudinally centrally located flexibleprojecting portion which, prior to release of said actuating biasmember, is situated beyond the other end of the syringe, such that aprimary movement of the plunger, under the bias of the actuating biasmember, will cause the projecting portion to bear against the other endof the syringe such that the syringe is moved from said first to saidsecond position, whereupon arresting of further movement of the syringe,results in the flexible portion collapsing inwardly so that it entersthe syringe, thus enabling the plunger to move by a secondary movement,within the syringe, into contact with and to act upon a plug to compressthe liquid within the syringe and cause expression of the liquid throughthe syringe needle.

With such an arrangement, the projecting portion will remain in itsprojecting position (in order to move the syringe from the first to thesecond position) until the force increases to such an extent whichallows the projecting portion to collapse inwardly so that the plungercan then move within the syringe to cause the liquid to be expressedthrough the syringe.

The projecting portion can comprise one or more flexible elbowsprojecting beyond the normal circumference of the rod, but compressibleinto said circumference. This could be in the form of two elbows definedeither side of a longitudinal slit in the rod. The elbows could bepre-formed as a pair of arms either side of the longitudinal slitbetween upper and lower solid portions of the rod.

Preferably the injection device will contain a return bias member actingbetween the syringe housing and the other end of the syringe to hold thesyringe retracted within the housing until the actuating bias member isreleased. One or more of the bias members provided within the housingcan be in the form of a coil spring.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be performed in various ways and a preferred examplethereof will now be described, with reference to the accompanyingdiagrammatic drawings, in which:

FIG. 1 is a sectional view through an injection device of this inventionprior to use; and

FIGS. 2 and 3 are similar views showing successive stages of operationof the injection member.

DESCRIPTION

The injection device shown in the drawings comprises a syringe 1 locatedwithin a protective housing 2. The syringe comprises a 3 incorporating aliquid dose held in place by a bung 4 and having a needle 5 throughwhich the dose can be ejected by applying pressure to the bung 4. The 3has an enlarged head 6. A plunger 7 is biased forwardly by a coil spring8, but is held back in a latched position (FIG. 1) until such time as atrigger shown schematically at 11 is actuated to release the plunger andthe spring 8. Prior to use the syringe 1 is held retracted in thehousing 2 by a coil spring 9.

It will be seen that the plunger 7 is in the form of a rod having acentral portion which defines a pair of projecting elbows 10. These canbe pre-formed as part of a moulded plunger 7. The projecting elbowportions 10 are flexible so that they can be moved inwardly to causethat portion of the rod to adopt a circumference similar to that of therest of the rod. As can be seen in FIG. 2, when the plunger is releasedand biased by the spring 8 the expanded region formed by the elbows 10rests against the head 6 of the 3 and the force provided is sufficientto compress the spring 9 until such time as the head 6 abuts the top ofthe housing 2, whereupon further movement of the 3 is arrested. Thecontinual bias created by the spring 8 then causes the elbows 10 to be20 compressed inwardly as they enter into the interior of the 3. Withthe elbows 10 in the collapsed state, the plunger can then moverelatively easily within the 3 so as to act upon the bung 4 and thuscause the contents of the syringe to be ejected through the needle 5.

The illustrated configuration of the plunger 7 provides severaltechnical advantages. It can be moulded integrally. Also the collapsingmovement of the projecting elbows provides an arrangement which canprovide a suitable injection force to cause the needle to enter the skinto a suitable depth, but then provide a relatively low drag against theinner wall of the syringe container so that the major portion of thethrust of the spring for the remainder of its stroke is applied to thebung 4. It will be appreciated that other configurations of collapsingprojection could be used in place of the collapsing elbows.

What is claimed is:
 1. An injection device for causing a dose of liquidto be ejected from the needle at one end of a syringe (1) located withina housing (2) of the device, the syringe being movable by a plunger (7),upon release of an actuating bias member (8) at one end of the housing(2), to move the syringe (1), from a first position wherein the needle(5) is shrouded by the housing (2), to a second position wherein theneedle projects from the other end of the housing, the plunger being inthe form of a rod with a longitudinally centrally located flexibleprojecting portion which, prior to release of said actuating biasmember, is situated beyond the other end (6) of the syringe (1), suchthat a primary movement of the plunger (7), under the bias of theactuating bias member (8), will cause the projecting portion (10) tobear against the other end (6) of the syringe such that the syringe ismoved from said first to said second position, whereupon arresting offurther movement of the syringe, results in the flexible portion (10)collapsing inwardly so that it enters the syringe, thus enabling theplunger (7) to move by a secondary movement, within the syringe, intocontact with and to act upon a plug (4) to compress the liquid withinthe syringe and cause expression of the liquid through the syringeneedle (5).